1. Field of the Invention
This invention relates to regeneration of an adsorbent. More particularly, this invention relates to a two step process for the regeneration of an adsorbent comprising a mixture of alumina and zeolite suitable for use as an adsorbent for ammonia.
2. Description of the Related Art
Waste streams from tanning processes usually contain ammonia, sulfides and dissolved organics due to the use of chemicals such as (NH.sub.4).sub.2 SO.sub.4 and NH.sub.4 Cl which are used in the tanning of hides and the organic residues from the hides.
Current commercially practiced methods for purifying waste streams from such processes employ precipitation techniques which are expensive and technically unsatisfactory. It is also known to individually remove some of the impurities found in such streams by use of adsorbents such as silica gel, activated alumina or zeolites.
In a copending Bush et al. application Ser. No. 877,554 entitled "Purification of Waste Stream From Tanning Process by Adsorption on an Adsorbent Comprising a Mixture of Alumina and Y Zeolite", filed on even date with this application and assigned to the assignee of this invention, cross-reference to which is hereby made, there is described and claimed a process for treatment of an aqueous effluent containing ammonia. In this process, an aqueous effluent, such as the effluent from a tanning process, containing ammonia and organic materials, is contacted by an adsorbent which comprises a mixture of alumina and a sodium type Y zeolite. This adsorbent mixture has been found to be particularly effective in removing ammonia from waste water.
When an adsorbent is used to remove impurities from a liquid in contact therewith, the adsorption capacity of the particular adsorbent is at some point reached. At this time, the adsorbent must be replaced either by discarding the adsorbent or by regenerating the material by stripping or desorbing the adsorbed material from the adsorbent. Environmental constraints as well as the chance to recover valuable materials for recycling make regeneration rather than discard the choice for spent or saturated adsorbent.
In the aforesaid copending application, reference is made to regeneration of the saturated adsorbent by treating the adsorbent with a base to desorb the ammonia (the ammonium ion) from the adsorbent mixture. While such regeneration is effective to remove much of the adsorbed ammonia, it has been found that the adsorption capacity for ammonia of the regenerated adsorbent is usually not as high as that of the original ammonia adsorption capacity of the adsorbent.
It has now been discovered that the ammonia adsorption capacity of an adsorbent comprising a mixture of alumina and Y type zeolite can be completely restored during regeneration to as good or better than the original ammonia adsorption capacity of the adsorbent mixture.